The discharge of rinsing solution in industrial processing especially in the electroplating processing, without any treatment, will cause serious environmental pollution, and hence is extremely harmful for human being and nature.
In recent years, on the one hand, technology revolution for electroplating promotes wide-range utilization of non-cyanide electroplating, low-chromium or non-chromium passivation, low concentration chromium plating, etc., thus reduces the extremely poisonous materials in rinsing water, but the waste water effluent still can not meet the requirement of effluent regulation. On the other hand, the treatment of the electroplating waste water by chemical and ion-exchange methods and corresponding equipments have been widely adopted in the world to reduce the concentration of poisonous materials to an allowable range.
However, in electroplating processing, each type of plating will produce about 1000 l/h waste water. Large quantity of waste water needs to be treated especially for those plants which conduct long period electroplating operation and multi-type plating operation.
In some plants the quantity of waste water amounts to tens thousand tons each month. At present, the electroplating waste effluent is strictly controlled in many countries, therefore, a large number of equipments for treating waste water is required, which corresponds an investment 1 to 1.2 times as much as that for electroplating processing line. Such a high investment for waste water treatment equipments makes it difficult to conduct electroplating processing not only for small plants but also for middle-scale plants. U.S. Pat. No. 4,595,474 disclosed a "Recovery System of Electroplating Solution". Based on the principle of siphonage, the liquid in rinse tank is transferred to the plating tank to make up the gradually decreased quantity of plating solution in the plating tank and to maintain the liquid level balance between plating tank and rinse tank, hence partially recovers the plating solution, reduces the concentration of poisonous materials in rinsing water effluent from the last rinse tank, and reduces the cost for the waste water treatment. Comparing with the traditional plating technology, this method is more or less effective in recovering plating solution and reducing the volume of waste water to be treated. However, in the electroplating process using such a system, the evaporation and consumption amount of plating solution and the recovery amount from rinse tank are hardly to balance between each other and a large quantity of waste water is still produced, which needs further treatment before discharge. The only advantage is that the volume of waste water to be treated is more or less reduced. The investment for treatment equipments and operating cost remain at high levels. Two main deficiencies can be summarized from that prior art as follows: firstly, the quantity of rinsing water for each type of plating is more than 500 l/h; secondly, the plating waste water still needs to be treated with waste water treating equipments.
In short, the prior arts has not coped with above-mentioned problems very successfully.